export const defaultNamespace = 'lf';
const statePrefix = 'is-';

const _bem = (
  namespace: string,
  block: string,
  blockSuffix: string,
  element: string,
  modifier: string
) => {
  let cls = `${namespace}-${block}`;
  if (blockSuffix) {
    cls += `-${blockSuffix}`;
  }
  if (element) {
    cls += `__${element}`;
  }
  if (modifier) {
    cls += `--${modifier}`;
  }
  return cls;
};

export const useNamespace = (block: string) => {
  const namespace = defaultNamespace;

  const b = (blockSuffix = '') => _bem(namespace, block, blockSuffix, '', '');
  const e = (element?: string) => (element ? _bem(namespace, block, '', element, '') : '');
  const m = (modifier?: string) => (modifier ? _bem(namespace, block, '', '', modifier) : '');

  const be = (blockSuffix?: string, element?: string) => (blockSuffix && element
    ? _bem(namespace, block, blockSuffix, element, '')
    : '');
  const em = (element?: string, modifier?: string) => (element && modifier
    ? _bem(namespace, block, '', element, modifier)
    : '');
  const bm = (blockSuffix?: string, modifier?: string) => (blockSuffix && modifier
    ? _bem(namespace, block, blockSuffix, '', modifier)
    : '');
  const bem = (blockSuffix?: string, element?: string, modifier?: string) => (blockSuffix && element && modifier
    ? _bem(namespace, block, blockSuffix, element, modifier)
    : '');

  const is = (name: string, ...args: [boolean | undefined] | []) => {
    const state = args.length >= 1 ? args[0]! : true; // '!' 后置为断言，表示args[0]不可能为undefined或者null
    return name && state ? `${statePrefix}${name}` : '';
  };

  /*
   * for css var
   * --#{$namespace}-xxx: value;
   */
  const cssVar = (object: Record<string, string>) => {
    const styles: Record<string, string> = {};
    for (const key in object) {
      if (object[key]) {
        styles[`--${namespace}-${key}`] = object[key];
      }
    }
    return styles;
  };
  // with block
  const cssVarBlock = (object: Record<string, string>) => {
    const styles: Record<string, string> = {};
    for (const key in object) {
      if (object[key]) {
        styles[`--${namespace}-${block}-${key}`] = object[key];
      }
    }
    return styles;
  };

  const cssVarName = (name: string) => `--${namespace}-${name}`;
  const cssVarBlockName = (name: string) => `--${namespace}-${block}-${name}`;

  return {
    namespace,
    b,
    e,
    m,
    be,
    em,
    bm,
    bem,
    is,

    // css
    cssVar,
    cssVarName,
    cssVarBlock,
    cssVarBlockName,
  };
};
